1. Field of the Invention
Embodiments of the invention related to a semiconductor device and method of manufacturing a semiconductor device.
2. Description of the Related Art
Commonly known semiconductor devices use a semiconductor material whose band gap is wider than that of silicon (Si) (hereinafter, “wide band gap semiconductor”) such as silicon carbide (SiC). When a high-voltage device is manufactured using a silicon carbide semiconductor and high voltage is applied, the electric field concentrates at an end of an element. Therefore, a breakdown voltage structure needs to be formed to mitigate the electric field. The surface of the breakdown voltage structure is generally coated with a protective film such as an oxide film. However, an interface state is formed at the interface between the semiconductor and the protective film and when high voltage is applied, a thin depletion layer spreads in the surface of the semiconductor toward the chip end under the influence of the interface state. The depletion layer reaches the chip end where the crystalline structure is in disarray from dicing and causes leak current. To prevent this phenomenon, a region referred to as a “channel stopper” and having a high impurity concentration is generally formed around the device to thereby suppress the spreading of the depletion layer to reduce the leak current (see, for example, Rottner, K., et al, “SiC power devices for high voltage applications”, Mater. Sci. Engineer. B, Vol. 61-62, p. 330-338, 1999).
In a silicon carbide semiconductor device, it is difficult to form a semiconductor region of an arbitrary conductivity type by diffusion and therefore, ion implantation is used. After the ion implantation, processing at a high temperature has to be further executed. Without this high temperature processing, the exchange with the atoms in the silicon carbide does not take place and no carrier is therefore generated and the region does not operate as a conductivity type semiconductor region.
When this high-temperature activation process is executed after the ion implantation of a high impurity concentration is executed, electrical properties are adversely affected consequent to a lattice defect present in the silicon carbide substrate (see, for example, Tsuji, T., et al, “Analyses of high leakage currents in Al+implanted 4H SiC pn diodes caused by threading screw dislocations”, Mater. Sci. Forum Vols. 645-648 (2010) p. 913-916). When a channel stopper whose impurity concentration needs to be a high concentration is formed as a measure against the above, lattice defects are generated to be leak sources. In this case, the leak is increased when the depletion layer generated due to the interface state reaches the channel stopper.